This invention concerns drives for agricultural machine elements and more particularly a variable speed drive especially useful for driving a harvesting machine element such as the threshing cylinder of a combine.
Variable speed drives for harvesting machine elements make it possible to adjust element speed to optimise performance in a particular operating condition or crop type. Thus, drive systems for combine harvester threshing cylinders commonly include a variable speed component such as an infinitely variable V-belt drive having, however, an inherently limited speed range.
The speed range available is sometimes extended by including a changeable gear drive in the drive system so that the infinitely variable speed feature is available in two or more ranges. U.S. Pat. No. 3,375,738 Love, also assigned to the assignee of the present invention, discloses a drive of this general type. However, the geared portions of known drive systems are generally somewhat complex and bulky, particularly in terms of axial extent. Typically, even in co-axial gear-driven sheave arrangements, the driven sheave is axially and structurally separated from the final drive gear assembly. Manufacturing cost of such drives is relatively high and their bulk limits their adaptability.